The present invention relates to a computer or the like capable of external communication and, more particularly, to a computer or the like, capable of connecting to a wireless LAN.
Computers, typically, by notebook-type personal computers (notebook PCs) can be connected a network such as a LAN (local Area Network) by an interface device called a NIC (network interface card) or a LAN adaptor. Modems were first used as interfaces connected to networks and the present dominant interfaces connected to networks are wired communication interfaces such as Token-Ring and Ethernet (trademark). However, wireless LANs are preferable in terms of avoidance of troublesome cable wiring and are expected to come into widespread use in the future with the rapid development of notebook PCs, portable telephones, mobile terminals such as PDAs, etc.
In recent years, a need has arisen in some cases of automatic diagnosis or maintenance operation executed on a disk storage system or the like to power-on a PC provided with a service processor without intervention of an operator. Also, in a company for example, there is a need to perform, for example, simultaneous rewriting of programs in a multiplicity of PCs in a system for the purpose of reducing the total cost of the system including the maintenance cost. In such a situation, it is required that each PC be powered on without intervention of an operator. Wake-on-LAN therefore attracts attention as one of network management functions. Wake-on-LAN starts up a PC by sending a particular packet (magic packet) from a network. Wake-on-LAN enables a PC to be powered on according to an instruction which is provided from a network by an operation at a remote place instead of an operator's manual power-on operation.
A conventional art is known which uses a system in which wakeup information can be contained in a frame control channel (FCCH) in a medium access control (MAC) frame transmitted from an access point (AP) in a wireless LAN for the purpose of minimizing the power consumption in a mobile terminal (MT) in the wireless LAN, the mobile terminal entering a sleeping state when the wakeup information is not contained (see, for example, patent document 1).    Patent document 1    PC (WO) 2002-541731 (pages 7 to 11, FIGS. 2 to 4)
With the rapidly increasing prevalence of wireless LANs in recent years, there has been an increasing demand for implementing also in wireless LANs Wake-on-LAN realized in the wired Ethernet LAN. As a method for implementing Wake-on-LAN in a wireless LAN, a method using a power save mode specified in standards related to the international standard IEEE802.11 is conceivable. More specifically, the power save mode specified in IEEE802.11 is enabled in a client PC (station) in a Wake-on-LAN waiting state. In this power save mode, the client PC is in a sleeping mode for a time period (DTIM (Delivery Traffic Indication Map) interval) set under an agreement between the client PC and an access point. When the access point receives a data packet addressed to the client PC, it buffers the data packet. The client PC wakes up (exits from power save mode) and checks information in DTIM frames whether any data packet addressed to it was received when it was in the sleep mode. If a received data packet addressed to the client PC exists, the client PC obtains the data from the access point. If there is no received data packet addressed to the client PC, the client PC again enters the sleeping mode in the next DTIM interval.
Power consumption is a hindrance to the implementation of Wake-on-LAN in a wireless LAN. While the power consumption in a state of waiting for a Wake-on-LAN packet in the wired Ethernet LAN is about 100 mW, an amount of power 12 times higher than this, i.e., 1.2 W or more, is consumed in the case where the current wireless LAN is used. That is, while the power consumption in a wireless LAN adaptor at the time of reception of a wireless frame is 600 mW, the power consumption at the time of transmission is considerably large, 1.2 to 1.5W. This is because a low-noise amplifier for amplifying a wireless signal at the time of transmission consumes a large mount of power. When a wireless frame is transmitted in the Wake-on-LAN standby state, the power consumption largely exceeds 660 mW specified in the mini PC specifications. Also, a large load is imposed on a power subsystem in a PC main unit. There is a need to change the hardware in order to ensure withstanding against the peak power in the standby state.
Also, the client PC must associate with the access point before entering the power save mode. To perform this association, it is necessary for the client PC to transmit a wireless frame to the access point. That is, there is also a problem that the client PC must transmit various wireless frames to enable use in Wake-on-LAN of the power save mode in accordance with the above-mentioned IEEE 802.11 specifications.
Further, in order to enter the Wake-on-LAN standby mode, the client PC must first identify the access point from which it receives a magic packet. It is therefore necessary for the client PC to start scanning for finding the access point. If the access point is not found, it must periodically repeat scanning. For scanning for finding the access point, transmission of a wireless frame is also required and there is a need to reduce the power consumption at the time of transmission of the wireless frame.
The present invention has been achieved to solve the above-described technical programs, and a purpose of the present invention is to enable a power supply for a system in a computer connected to a wireless LAN to be turned on the basis of a signal from the wireless LAN side.
Another purpose of the present invention is to reduce the power consumption in a computer having the function of connecting to a wireless LAN.
Still another purpose of the present invention is to enable a computer having a wireless LAN function in accordance with the IEEE 802.11 related standards to receive a broadcast/multicast frame without performing handshaking with an access point.